EFFECTS OF ORGANIZED MEDIA ON THE EXCITED-STATE PROTON-TRANSFER IN 2-(2'-PYRIDYL)BENZIMIDAZOLE

Absorption and fluorescence characteristics of 2-(2'-pyridyl)benzimida zole (2-PBI) are studied in the presence of alpha- and beta-cyclodextr ins (CD) in aqueous solution at two different pHs. Steady-state and ti me-resolved fluorescence measurements are used for the investigation o f the effect of organised media on the excited-state proton transfer r eaction in 2-PBI. Semi-empirical CI calculation for the geometry of th e molecule reveals that the 2-PBI molecule may be involved in host-gue st complex formation with alpha-CD and beta-CD in different configurat ions. NMR measurements corroborate this, providing information about t he orientation of the 2-PBI molecule inside the cavity of the CDs. No complex formation was evident in gamma-CD owing to its larger cavity d imension compared to the size of the 2-PBI molecule.